Glucosinolates
Glucosnolates is made out of sulfer, nitrogen and glucose. Vegetables in the family of cabbage such as Chinese bok choy contains protective phytochemicals called glucosinolates that assist the body to get rid of carcinogens. Glucosinolates are acknowledged for their toxic effects in humans if too much is consumed. At a low level of toxic consumption, their hydrolytic and metabolic products protects us against chemically-induced carcinogens by blocking the initiation of tumors in a variety of liver, colon, pancreas and mammary gland.
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Citations:
http://upload.wikimedia.org/wikipedia/commons/thumb/1/13/Glucosinolate-skeletal.png/800px-Glucosinolate-skeletal.png
http://www.bcm.edu/cnrc/consumer/nyc/vol3_03/glucosinolates.htm